Question

A triangle is formed by the x-axis, the y-axis and the line y = ax + b. If a = -b, then what is the volume of the cone generated by rotating this triangle around y-axis.

a) pi/9
b) (pi/3)a
c) pi
d)3pi

Answer 1

b is the height
the radius is 1

Answer 2

umm.. i don't get it :s

Answer 3

Y = ax + b becomes
y = -bx + b
y/b = -x + 1
from this we can see that intercept on y axis = 1 and this is the height of the cone.
when y = 0, x = 1 and that is the radius of the base of the cone

Answer 4

sorry secret there is an error in the above
the radius of the cone is 1
but i'll take another look at the height

Answer 5

the height is b as him said - the intercept on the x axis is -b1/2
so the volume is (1/3) pi r^2 h
= (1/3) pi 1^2 * -b
=(1/3)* pi * a
= (pi/3) * a which is b) on the list

Answer 6

i'm going crazy here correction of the first line
the intercept on the y axis is -b!!

Answer 7

i've got it right at last

Answer 8

oh, coool. NOW i really understand it.
thanks guys!

Answer 9

yw